A: Yes, with the right considerations, a pond with goldfish and koi is absolutely doable. While the two fish have some notable differences, it is possible to create an environment where both can thrive.
What is the Difference Between Koi and Goldfish?
If you are going to maintain a pond with koi and goldfish, it’s helpful to be able to tell them apart. Fortunately, there are a few telltale traits that make this pretty easy.
- Size. Koi are larger than goldfish. Pond goldfish tend to be larger than aquarium goldfish, but they are still usually smaller than a full-grown koi. With enough space, food, and a healthy environment, goldfish can grow to over a foot long. An adult koi, meanwhile, can range from one to three feet long, depending on the type. Domestic koi are generally on the smaller side of that range.
- Barbels. One of the quickest ways to tell the two apart is to look at the mouth. Koi have small, horn-like protrusions on either side of their mouth. Known as barbels, these are sensory organs that help koi search for food. Goldfish do not have barbels.
- Shape Koi are stout and muscular. Goldfish, even when they are a similar length to koi, have a more narrow shape.
- Activity. Goldfish are not as active as koi. This is especially apparent during mealtimes when koi can become aggressive due to their competitive nature surrounding food.
Caring for Koi and Goldfish
For all of their differences, you may be wondering– how can koi and goldfish live together in the same pond? Fortunately, their environmental and care requirements are quite similar.
- Temperature. The optimal temperature for koi and goldfish is between 59–77°F. At colder temperatures, both fish enter a semi-dormant state. During this time, they stick to the bottom of the pond and conserve energy. It is not necessary to feed either fish when they are dormant.
- pH Levels. Ideally, fish that are kept in the same space have similar pH requirements. Koi thrive at pH levels between 7 and 8.6. Pond goldfish require a pH between 6.5 and 7.5.
- Plant life. Both fish need access to shelter and shade, and plant life is an excellent way to provide that. When creating a koi and goldfish pond, make sure there are plenty of plants.
- Food. Koi do best on a more protein-rich diet than goldfish, but there are some foods that can meet the nutritional demands of both types of fish. Look for a balanced formula that is easy to digest such as The Pond Guy’s Staple Fish Food.
Common Koi and Goldfish Pond Mistakes
If you do decide to mix koi and goldfish, there are a few things to keep in mind.
- Avoid overcrowding. Too many fish in a pond can create a poor environment for your fish, water quality issues, and a breeding ground for algae. The more fish you have, the more waste they produce, which often leads to common fish diseases and health problems. For koi, the magic number is 1-2 fish per 200 gallons of water. With goldfish in pond environments, you can have 2-3 fish per 200 gallons of water. In general, aim for one foot of fish for every 100 gallons of water, and remember that it’s better to overestimate how much space your fish need. Keeping too many in cramped quarters can lead to aggressive behavior and bullying.
- Be mindful of size. There are over 200 types of goldfish and 100 types of koi. Try to keep fish that are similar in size because koi and goldfish that are close in size are much better able to co-exist peacefully. After all, a small fancy goldfish may serve as a meal for a larger domestic koi.
- Monitor mealtimes. Koi love to eat and they don’t share well. You will need to make sure that the goldfish in your pond are still able to access food. One way to do this is by feeding your fish in different areas of the pond. Drop food pellets or flakes in one area and wait until the Koi take notice. Once they swim to the food, drop a little more in another part of the pond for the goldfish.
Maintaining a Goldfish and Koi Pond
Koi and pond goldfish may be hardy but they do much better in a clean, balanced pond environment. At a minimum, your pond should be thoroughly cleaned once per year, and spring is the best time for a cleanout. We recommend spring and fall cleanouts, with summer cleanouts as needed.
A full pond cleaning involves changing out the pond’s water, removing dead plants, and skimming debris off the water's surface. One thing to note is that you don’t need to change out all the pond’s water at once. Instead, aim to drain and replace 50% of the pond’s water with each cleaning. If the water is dirtier than normal or if you are only cleaning the pond once per year, replace 75% of the pond’s water, instead.
After partially draining your pond, it’s also a good idea to inspect the filter and aeration system. Make sure both are free from debris and in good condition and replace any broken or worn out parts.
With the right environment and care, koi and goldfish can easily live together. If you need additional support, the experts at The Pond Guy are available to help.